The present invention relates generally to a nonvolatile semiconductor memory, and more particularly, to an integrated circuit (IC) device with expandable nonvolatile memory.
Along with the development of compact electronic products, nonvolatile memories have been widely used. FIG. 1 shows a structure of a nonvolatile memory such as a conventional flash memory, electrically erasable programmable read only memory (EEPROM) and multi-time programming (MTP) memory. It includes a nonvolatile memory circuit 10, a control unit 22 and a voltage generator 24, in which the nonvolatile memory circuit 10 comprises a memory array 11 for data storage, an X decoder and driver 12 and a Y decoder and driver 13 for memory unit selection, a Y pass gate 14 for control of accessing data in the memory array 11, a sense amplifier and programming circuit 15 for reading and writing data, and an input/output (I/O) buffer 16 to serve as an interface between the memory and exterior. The control unit 22 generates various signals for the memory when data reading and memory programming and erasing. In addition, the control unit 22 transmits various corresponding signals to the programming circuit on the basis of the sense amplifier in programming and erasing operations. In response to program, erase and correction operations, the voltage generator 24 generates various corresponding voltages such as +10 V,xe2x88x9210 V,+5 V, etc., which can be generated by a voltage rising circuit or a voltage divider.
The memory capacity of a nonvolatile memory IC is fixed. A higher capacity means more advanced fabrication technique, lower yield and higher cost. Multiple nonvolatile ICs are therefore connected in series for the requirement of a higher memory capacity. However, waste is also occurred for such circumstances. Only the control unit and voltage generator of the selected nonvolatile memory IC are in operation when reading data or in programming. For example, in the operation of programming, data are sequentially, written into memory units and the memory units are also sequentially verified, that is, not all control units and voltage generators in a group of serial nonvolatile memory ICs are in operation at the same time. As a result, such multiple circuits in a group of serial nonvolatile memory ICs are wasteful, and become more significant with the increment of serial ICs. In the case where control units 22 and voltage generators 24 occupy a lager portion of chip area, decrease in the number of the wasteful circuits can reduce the chip size and its fabrication cost.
On the other hand, in an IC including nonvolatile memories, for instance in a microcontroller or microcomputer, various memory capacities are requested for different applications. It is therefore necessary to fabricate microcontrollers or microcomputers in a specific type with nonvolatile memories of different capacities adaptively for different applications. Contrarily, various applications can be obtained in reduced cost if a microcontroller or microcomputer is employed adaptively in connection with external nonvolatile memory ICs in which control units and voltage generators are removed from each single nonvolatile memory IC.
It is therefore an object of the present invention to disclose an expandable nonvolatile memory device.
Another object of the present invention is to provide an IC device with expandable nonvolatile memory to overcome the shortcomings of advanced technique, low yield and high cost due to high memory capacity.
According to the present invention, a semiconductor device comprises at least one nonvolatile memory IC in which the control unit and voltage generator for the memory operation are independently integrated into a common circuit and shared by all nonvolatile memory ICs.
In one aspect of the present invention, multiple circuits and the chip area they occupy in an IC device with expandable nonvolatile memory can be reduced.
In another aspect of the present invention, flexibility is obtained for the memory expansion in an IC device.
Standardizations of IC devices with nonvolatile memory are available for various applications according to the present invention.